California’s junior US Senator issued a strong warning to House Republicans: don’t handcuff the federal Environmental Protection Agency. And by the way, hands off the highway trust fund.

Nearly 50 House Republicans introduced a bill on opening day to stop the Environmental Protection Agency from regulating greenhouse gas emissions.

Sen. Barbara Boxer, D-California, who heads the Senate Environment and Public Works Committee, says she’ll fight efforts to stall the agency.

She says earlier, bipartisan efforts to cut smog led to cleaner air and greater productivity.

"If you can’t breathe, you can’t work," she says, "and if anyone in Congress tries to move toward dirty air policies, I will take that straight to the American people and do everything in my power to stop them."

Boxer also warned Republicans against using gas taxes for anything other than infrastructure projects. One of the rules the House passed Wednesday opens the door to tapping the highway trust fund for non-infrastructure purposes - like balancing the federal budget.

Boxer says the highway trust fund used to have a firewall.

"And no one can steal the money from it for other uses or leave it just sitting there; the point of it is, it’s supposed to meet needs of people."

The Senate Environment and Public Works Committee begins hearings later this month on the new multi-year transportation bill. Gasoline taxes would pay for road and bridge repairs, mass transit, and other infrastructure projects.